1. Field of the Invention
The invention relates to a method of regenerating brake linings, particularly for railway vehicles.
2. Description of the Related Art
Brake linings have a friction lining attached to a lining carrier. The friction lining layer is worn away during the braking process as a result of the frictional loading so that replacement of the used brake lining becomes necessary. Brake linings are commonly replaced before the friction lining layer has been completely removed at the most strongly worn position. For reasons of safety brake linings are generally replaced considerably before they are fully worn. For instance, linings on railway vehicles are commonly replaced when their friction lining layer has been about 50% used up.
Although a large proportion of the friction lining layer thus remains unused, the used brake linings are subjected to material recycling.
It is the object of the invention to provide a method of regenerating brake linings, particularly for railway vehicles, that permits more economical recycling of the used brake linings.
This object is solved in accordance with the invention by a method for regenerating brake linings, particularly for railway vehicles, in which a friction lining layer is machined from its worn surface and provided with a three-dimensional surface profile, the profiled surface is coated with a bonding agent and thereafter a fresh friction lining composition is pressed on.
This method has the advantage by comparison with the known methods that a substantially greater proportion of the remainder of the friction lining, which has not been worn away, can be reused for the regenerated brake lining. Any oblique wear which potentially occurs, i.e. non-uniform abrasion of the old friction lining layer, is fully compensated for by the regenerating method in accordance with the invention. Furthermore, the dust or chippings produced by grinding away or milling away the surface of the friction lining can be reused, for instance for road building purposes.
The three-dimensional surface profile creates a toothed transition between the old friction lining composition and the newly pressed on composition. The lining thus formed can be worn away over the newly applied layer of friction lining composition, whereby use of the entire new lining thickness is rendered possible. At no stage of the abrasion is a surface layer of which a major proportion comprises bonding agent used for braking purposes.
In one embodiment of the method in accordance with the invention the worn surface is machined by profile grinding or profile milling such that a profiled surface with a tooth-shaped, trapezoidal or meander-shaped profile perpendicular to the surface is produced, the profile extending, at least in sections, in a first direction on the surface. In another embodiment the worn surface is machined by coarse grinding such that an irregular surface structure with substantially elongate recesses is produced, the recesses which are formed extending, at least in sections, substantially in a first direction. This machining process is performed successively in two intersecting directions in a further embodiment. In the embodiments of the method in accordance with the invention referred to above a surface structure is produced which affords a large area and into which the fresh friction lining, which is subsequently pressed on, engages, so that shearing away of the fresh lining is prevented. The selection between the aforementioned surface structures or profiles is effected in dependence on the machining process selected, particularly the tools which are used and the desired field of application of the regenerated brake linings.
An advantageous embodiment of the invention is characterised in that the profile depth of the surface structure is in the region of about 1 to 30 mm, preferably 5 to 20 mm. The profile depth of the surface structure is so selected that there is a minimal risk of shearing away and a good connection between the old friction lining and the newly applied friction lining composition. On the other hand, the profile depth is so selected that as large a proportion as possible of the old friction lining composition can be reused, i.e. that as small a proportion as possible is removed by the grinding process.
If the new friction lining layer is worn down beyond the transition between the new and old friction lining compositions, the depth of the profile results in the surface of the friction lining never having a large proportion of bonding agent.
In a preferred embodiment of the method in accordance with the invention a direction transverse, preferably at right angles, to the direction of the main loading of the friction lining during the braking process is selected as the first direction. The risk of the newly applied friction lining composition shearing away from the old friction lining composition is thereby further reduced.
In one embodiment of the method the first direction is altered in a plurality of adjoining sections of the friction lining surface. This feature further improves both the adhesion and also the shear resistance of the applied friction lining composition.
One embodiment of the invention is characterised in that a worn friction lining layer applied to a metal plate is worn down to a predetermined residual thickness such that the plate constitutes, together with the remaining friction lining layer, a sufficiently mechanically stable structure for the further method steps. This exemplary embodiment finds application particularly in linings for railway vehicles or other large linings with relatively thin carrier plates. The thin plate together with a sufficiently thick residual lining serve as a carrier for the regenerated brake lining. Particularly in the case of those brake linings in which the lining carrier is a thin plate and in which the friction lining composition thus serves additionally to mechanically stabilise the structure, the brake linings are replaced at a relatively early time at which the remaining frictional lining is still sufficiently thick to stabilise the structure. In this application about 30 to 60% of the friction lining composition is saved by the method in accordance with the invention.
A substance containing phenol resin or rubber is preferably used as the bonding agent in the method in accordance with the invention.
Further advantageous embodiments of the invention are characterised in the dependent claims.